Pulse distributor, including electric discharge devices



July 14, 1953 A. H. REEVES 2,645,680

PULSE DISTRIBUTOR, INCLUDING ELECTRIC DISCHARGE DEVICES Filed 001?. 5,1947 3 Sheets-Sheet l 345678 Q/O/l/Z Inventor -ALEC H-REEVES A ilorneyJuly 14, 1953 R E 2,645,

PULSE DISTRIBUTOR, INCLUDING ELECTRIC I DISCHARGE DEVICES Filed Oct. 5,1947 s Sheets-Sheet 2;

- /3 75 /4 /a F/ G .2 f I K 2 MASTER a 4 5s 7 s even/2 PULSE GENERATOR{v0 36 I T- A0072 AUDIO 2 ifs/ TPU 7 OUTPUT Attorney July 14, 1953 A. H.REEVES 2,645,630 PULSE DISTRIBUTOR, INCLUDING ELECTRIC DISCHARGE DEVICESFiled Oct. 5, 1947 1 3 Sheets-Sheet 3 46 MASTER 45 PULSE GENE/PATCH SAW700m 1 PULS 75o film/O SHAPE/P INPUT B SBAP Inventor ALEC l-LRgEV ESAttorney Patented July 14, 1953 PULSE DISTRIBUTOR, INCLUDING ELEC- TRICDISCHARGE DEVICES Alec Harley Reeves, London, England, assignor f tolnternational Standard ElectricCorporation,

New York, N. Y., a corporation of Delaware Application October 3, 1947,Serial No. 777,818 In Great Britain October 3, 1946 This inventionrelates to pulse distributors of the type which distribute individualpulses in a pulse train between a number of individual circuits.

The object of the invention is to apply novel means to this purpose.

According to one of its aspects the invention consists of l apulse'distributor comprising a plurality of gaseous electric dischargegaps adapted ;to fire in succession in' a predetermined order inresponse to incoming pulses of electrical energy applied in common tothe said gaps and individual circuit being connectedto each gap for thetransmission of an outgoing pulse when the associated gap fires inresponse to an incoming pulse. a I

According to another of its aspects the invention consists of a pulsedistributor comprising a cold cathode gaseous discharge tube having aplurality of gaps adapted to fire in succession in a predetermined orderin response to incoming pulses of electrical energy applied in common tothe said gaps, an individual circuit being connected to each gap for-thetransmission of an outgoing pulse each time the associated gap fires inresponse toan incoming pulse.

Certain embodiments of theinventicn will now be described in relation tothe accompanying drawings in which:

Fig. 1 is a circuit diagram of a simple form of distributor, using amulti-gap gaseous discharge tube, suitable for distributing theindividual pulses of a train of pulses amongst a number of individualcircuits. v

Fig. 2 is a circuit diagram of a more elaborate form of distributorperforming function analogous to those of the distributor illustrated inFig. 1. V

Fig. 3 is a c'ircuitdiagram of a distributor suitable ,for generating arepeated pulse train, each pulse of a train being'under the control .ofan individual circuit.

These three embodiments make use of gaseous discharge tubes of the typehaving a number of gaps adapted to fire in succession in response tobeing separately ledout of the tube, so that an individual circuit canbe associated with each gap though the saidpulses are applied to all incommon.

Tubes'oi this type are described in specification -No. 763,655 filedJuly25,1947of Reeves 25 8 Claims. (01. 17915) there wouldbe no guaranteethat the starting gap scription thereof will now be given.

forGaseous Discharge Tubes and a brief de- In this specification thereis described cold cathode gaseous discharge tubes having a number ofdischarge gaps which fire in succession in a predetermined order, onapplication of pulses to the said gaps in common, due to ionisationbf anunfiredgap caused by the discharge in an ad joining fired gap. A firstpulse applied to the tube will fire only a predetermined gap called thestarting gapand various alternative measures to ensure this include thecloser spacing of the electrodes of the starting gap in comparison withthe other gaps, a bias potential applied to the starting gap only,

or the provision of a a permanently discharging gap, called a pilot gap,adjoining the starting gap, causing this gap to be permanently ionised.

After a sequence of discharges of the gaps of.

the tube, and when the last gap' in the predetermined order) hasfired,all discharges are extinguished and the tube isallowed to deionisebefore the commencement of another firing cycle.

If it is required to operate such a tube from a continuous sequence ofregularly spaced pulses, a limit is set to the permissable frequency ofpulse repetition by the need for a time interval between pulses, longenough to allow the gaps to become deionised (except the starting gapwhen a pilot gap is provided as previously described) If gaps (exceptaforesaid) remained ionised,

would fire first, in preference to the others, in a second or subsequentcycle of pulses nor that the predetermined firing order would bemaintained.

To enable'higher pulse rates to be used, measures to reduce deionisingtime may be taken and this may be done by the use of special gasatmospheres in the tube.

Alternatively it may be-arranged to ensure that one or more pulsessucceeding that which fires the last gap,.are prevented fromfiring anygaps in the tube so that a time longer than the interpulse interval isallowed for deionisation of the gas in the gaps. 7

Methods of doing this are described in-U. S. Patent No.2,516,915issuedAugust 1, 1950 ,of A. H. Reeves 29 for Gaseous DischargeDevice where (inter alia) the reduction of. the inter electrodevoltage,so that pulses do not reach first pulse of the next cycle.

decay of the memory effect will pass down the gaps of the tube in thepredetermined firing order,

, With such a potential applied, gaps once fired will continue todischarge and at the end .ofa

' cycle, all will be discharging and must be extinguished'before thenext operation cycle of the tube. There are various ways of doing this,one of which is used in the embodiments of the in'-' vention to bedescribed. I

If no such discharge-maintaining potential is applied, discharges willcollapse between pulses, during the firing cycle of thetube and theinterval between pulses must not be so long that the ionisation can fallbelow the level necessary to secure sequential firing.

This involves the use of pulse rates such that the tube has not time tobecome deionised between consecutive pulses at the end of the firingcycleafter extinguishment of the discharges, and measures such as thosedescribed in said U. S. Patent No. 2,516,915 become essential.

A phenomenon occuring in multi-gap tubes of this type, is calledthe'Memory effect.

This effect consists of a rise in the voltage required to fire a gap,which follows an extinguished discharge in that gap. when certainelectrode materials and gasses are used in the construction thereof.

If tubes possessing this feature, are supplied with pulses to theirgaps, in common, and with no constant discharge-maintaining potential, agap once fired, will ionise the adjacent unfired gap and extinguish atthe end of the pulse which firedit. The next pulse will fire the ionisedadjacent unfired gap but will not refire the extinguishedgap owing tothe said rise in its critical firing voltage, it being arranged that thepulse amplitude is below such critical voltage.

This memory effect persists long enough to ensure that gaps once fired,will not again fire during the firing cycle ofthe tube, but when allgaps have fired and all possess the memory effect the first gap torecover will be that which has been extinguished for the longest time,i. e. the starting gap, and this alone will fire on the inadvance'of'the firing sequence so that all in turn are ready to firefrom successive pulses.

4 l3 to the positive pole ofa battery l4 which may be regarded asrepresenting any" convenient source of direct current supply. r

The various cathodes are separately led out of the tube and each isexternally connected through an individual resistance and transformer inseries to a common connection leading to the negative .pole of batteryI4. Only one such resistance and transformer l5 and I8 respectively arenected to the secondary winding of the transformer.

A correspondin 7 A small bias may be applied to the starting gapto malequite sure that the sequence starts with that gap in cycles afer thefirst but this bias must not be large enough to leave the starting gappermanently discharging. It is also an advantage to insert arelatively'large resistanceload in series with one of the common pulsefeed connections to the gaps so that immediately on the firing of onegap, the increased voltage drop in the re sistance makes it impossiblefor another gap to fire from the same pulse; p Y,

I This enables the'tube' to be worked at a lower level of discriminationdue to memory effect between gaps and still secure the correct firingorder.

In Fig. 1 a gaseous discharge tube I has a common anode 2 consisting ofa straight bar or strip" and a series of individual cathodes in theform' of rods or strips at right angles to the anode and spacedtherefrom at one end of each cathode,

so as to define'disch'arge gaps, the tube illustrated having tencathodes and ten gaps 3, 4, 5, 6, I, 8,

9, l0, u and I2.

Anode! is connected through an impedance shown in the drawing terminal19 being con- All cathodes are connected to similar individual circuits.The potential applied to the gaps of the tubes by battery i4 is suchthat it cannot by itself initiate a discharge in any of the gaps but issufficient to maintain a discharge, once initiated.

vPositive pulses are applied to the anode of the tube through feedcondenser Hi from a common busbar l1. 7

- The pulses from If! consist of repeated trains of l consecutive pulsesand the gaps fire in turn from successive pulses until all are fired.

A gap once fired, continues to discharge till all have fired, due tobattery I4.

When all gaps have fired, they must be extinguished and allowed todeionise before the next firing cycle can commence; V

There are various ways of extinguishing the discharges but it isproposed in this and theother embodiments to be described, to provide apulse (hereinafter called the quenching pulse), of

the opposite polarity to that of thepulses (hereinafter called thefiring pulses), which fire the gaps.

These quenching pulses will oppose battery l4 and reduce theinter-electrode potential-to that which produces the requiredspeed ofdeionisa- "be some variation in the output as between the differenttransformers and where this is important, a differentiating networkmaybe introduced so that only the inception of the discharge isrecorded.

It is contemplated that the individual pulses from the busbar, may carrymodulation of .some kind, and it has been found that, with pulse ratessuch that a gap fires at rates up to about 1000 times per second, and;its corresponding firing pulse is modulated at some frequency, a lowfrequency transformer will give an output consisting substantially ofsuch modulating frequency, the pulses component being lost in' thetransformer, and this irrespectiveof the different discharge duration ofthe difier'ent cathodes.

' For higher frequencies it is preferable touse A Similar tubeto thatillustrated in Fig. l is 'usedandcorresponding items of thetube and itsassociated circuits are given the same reference numerals inbothfigures.

The cathodes of the tube have separate individual circuits as before,though here two of them are shown (those of the first and last cathodes)and one consists of resistance I and transformer 'a gate to permit thepassage of one pulse in each cycle of a continuous pulse sequence, andto dea continuousconducting path and may be made through condensers forinstance. It is possible to separate the gate and busbar circuits fromthe modulate that pulse, where it is-modulated, give an output at themodulating frequency. 7

The associated gap of the tube provides the gating impulse.

The discharges in the tube are controlled by pulses from a master pulsegenerator 45 WhlCh is synchronized with the pulses from the busbar 46and, in certain circumstances, both may be derived from a common source,though it only necessary to have a distinctive feature 1n one pulse ofthe pulse trains from the busbar (such as the quenching pulse on ll inFig. 1 for 1nstance) to enable a separate pulsegenerator 45 i to be keptin step with the pulses from the busbar.

' sociated gaps, and all simultaneously pass a negative pulse on thequenching of the tube. This negative pulse is ignored by thegate'devices as they incorporate a rectifier and in any event,

there will probably be no pulse from the busbar at these moments and thedevices need pulses from both sources to actuate them. I

Eachgate device has a condenser 25 and a resistance 26 which improve thepulse shape delivered by the associated cathode transformer and alsodecouple the transformer circuit from the busbar.

The busbar is also connected to each gate device through an individualcondenser 34 and resistance 35 whichare generally chosen so as not toalter the wave form of the busbar pulses.

Outlets to gate devices associated with intermediate gaps of the tubeare indicated by the arrows 31, 38, 39, '40, .42, and 44, these gatedevices and the details of the cathode circuits of y the associated tubegaps being omitted to simplify the drawing. v

.In each gate device there is a closed circuit consisting of a rectifier21, the primary winding of a low frequency transformer 36, a battery 3 Iand a and 28.

In a working circuit, of course there will be a common point, probablyearthed to which will be connected the negative side of master pulsegenerator 45, the negative pole of battery I4 in the tube circuit, andthe junction o'f'28, 29 and 3|. in the gate device and a secondconductor of the busbar. Theseconnections need not provide battery 3|.

cient to open the rectifier 21.

would have a similar effect.

tube circuits by using-separate earths for each by taking two leads fromthe secondary windings of the cathode transformers (20-22 etc.) insteadof earthing one side of these secondaries.

Rectifier 2'! is normally 'biassed to cut ofi by Pulses from the busbarare of positive polarity tending to open the rectifier but being ofinsufficient amplitude to do so by themselves. When the associated gapfires the pulse from 26, added from the pulse from 35 is sufii- It isarranged that the pulsefrom a cathode slightly leads the correspondingpulse from the busbar and only on the inception of the latter, is

.the rectifier opened. The pulse overlap is arranged to terminate withthe end of the tube pulse- The busbarpulse may be modulated in time orduration, but the tube pulse has constant timing, so that theperiodduring which. the rectifier is open commences at the varying time of thebusbar pulse and ends with the constant trailing edge of the tube pulse,so that a pulse flows in the closed circuitmodulated in duration inconformity with time of duration modulation the fundamental and lowerharmoniesof the pulse repetition frequency of the pulses in the closedcircuit. Time or duration modulation of the busbar pulses, in eithercase appears as duration modulation of the pulses in the closed circuit.This modulation can be regarded as a variation in the on-off ratio ofthese pulses and it is well known that a variation of this ratio variesthe amplitude of thefundamental component of the pulse-waveform.

The transformer used is preferably one with a frequency characteristicsuch that it attenuates the harmonies more than this fundamental, and

theaddition of a low pass filter 32, between the secondary winding of 30and terminals 36, produces an output at terminals 36 containing substantially themodulating frequency only. I

Amplitude modulation of the busbar pulses The embodiment illustrated inFig. 3 is very similar to that in Fig. 2 corresponding components aregiven the same reference numerals in the two figures.

The differences consist of the addition of a transformer 4'! in seriesin the gate device, closed circuit and the substitution in place of theconnection through 34 and 35 from the busbar of a connection throughcondenser 49 and resistance 48, from a saw tooth pulse shaper 50 whichmodifies the pulses of the master pulse generator 45, to saw toothwaveform. The busbar is connected to the secondary of transformer 41.

A modulating frequency is applied to terminals 36 instead of being takentherefrom.

Three potentials are simultaneously applied to the rectifier 21, firstpulses from the associated cathode of tube I, secondly the saw toothpulses from 55 and thirdly the instantaneous amplitude of the modulatingwave from terminals 36. At a certain point in the potential rise of thesaw tooth waveform, a potential suflicient to open rectifier 21, will beapplied to the closed circuit, and current will flow in the circuit. Itwill generally be arranged that the current will always stop at aconstant time coinciding with the end of the saw tooth pulse since thecathode pulse Will be of longer duration in the case of earlier firingcathodes.

The time at which the rectifier opens will of course be influenced bythe contribution to the total voltage across the rectifier, of themodulating wave from 36, and the leading edge of the resulting pulse inthe closed circuit, will be modu-' lated in time at the modulatingfrequency.

The output of 41 applied to the busbar will tend to be differentiated bythe transformer 41 to produce a pulse at the beginning of the closedcircuit pulse and a pulse of opposite polarity at the end of the closedcircuit pulse. If it is necessary to modify this wave form either toreshape the first pulse in the busbar or to eliminate the reverse pulsefollowing'it, or both, a single pulse shaping circuit on the busbar canperform this function for all pulses, and separate pulse shapingcircuits for all gate devices are unnecessary.

Taking Figs. 2 and 3 together therefore, the former provides a means oftaking repeating trains of pulses from a common source (the busbar) anddistributing them amongst various individual outlets (connected toterminals 36 of the various gate devices associated with variousvidualpulse in pulse trains applied-to the busbar.

It is envisaged that such devices may be used in a communication systemenabling several physical channels to communicate with a correspondingnumber of physical channels, over a common connecting link (the busbarwith or without intermediate apparatus) on a time division pulsemultiplex basis. In specification No. 794,724 filed December 30, 1947 ofD. H. Ransom- W. L. Roberts-R. H. Taplin 14-1-1 for Pulse Time PositionSwitching System a system of this nature is described wherein physicalcircuits are connected to scanned elements of a distributor, on thescanning element of which, the various physical channels are representedby individual pulses in a repeating pulse train. After passing throughlinefinder circuits and selection circuits, the common output appearsagain on the scanning member of a second distributor whose scannedelements are connected to individual physical channels. The devicesillustrated in Figs. 2 and 3 could be used in the role of thedistributors mentioned in that specification.

Tubes of the type described having the memory elfect may be used withadvantage in the embodiments described and have the advantage, sinceeach gapof the tube extinguishes, at

the end of the pulse which fires it and fires once only during a firingcycle of the tube, that pulse shaping measures and measures to suppressthe end-of-pulse output are unnecessary.

It also has other advantages including increased tube life since allgaps fire only once per firing cycle of the tube, for the duration oftheir firing pulses only, instead of continuing to discharge during thewhole firing sequence of the tube.

The omission of the maintaining potential .with a non-memory tube ispossible but presents .the difliculty that a gap fires repeatedly fromeach pulse subsequent to that which first fired it, during each firingcycle of the tube and measures are required to enable only the firstfiring to be recorded by the individual gap circuits.

The use of the expedients outlined in said U. S. Patent No. 2,516,915where one or more pulses are prevented from affecting the tubeafter thecompletion of a firing cycle, to allow extra time for deionisation,present no complication in the embodiments described, but of course,potential channels in the pulse cycle time are waste'd'to the extent ofthe pulses prevented from affecting the tube. Actually in thearrangements described, these pulses would preferably not be generatedby the master pulse generator.

There are applications where such a pause at the end of a pulse train isnecessary for other reasons and where this is the case, the expedientsin that specification may be used with advantage to enable any givendesign of tube to cope with a higher pulse rate than it could handle ifit had to become deionised during the normal interpulse interval.

It will have been observed that, whilst the arrangement of Fig. 2 has acorresponding simple or basic equivalent in the arrangement of Fig. 1 nosuch equivalent has been'shown for Fig. 3.

Such an equivalent may be simply devised by applying a saw tooth pulsesequence, such as that derived from 50 in Fig. 3, to the pulse feedcondenser l6 in Fig. 1, in place of the pulses from the busbar.

A transformer capable of passing pulses would then be substituted forl8, with its primary winding in series with the cathodec'ircuit; and itssecondary connected to the busbar'through suitable decoupling componentsto prevent interaction amongst the transformers associated with othercathodes, similarly connected to the busbar.

' Modulation could be impressed upon the pulses applied to the busbar bythe use of low frequency transformers, one in series with each cathodecircuit, the modulating signals being applied to the primaries of thesetransformers.

It should be arranged that the interelectrode potential across each gapreaches the critical value at which the gap will fire, at some timeduring the rising voltage of the saw tooth pulse applied to the gap, theexact instant of firing being determined by the modulating voltage inthe secondary of the said low frequency transformer which according toits instantaneous value will delay or accelerate the attainment of thecritical firing potential of the gap.

It is possible in certain circumstances to apply rectangular pulses tothe gaps of the tube instead of saw tooth pulses and still achievemodulation of the output pulses by means such as that just described.

This arises from the fact, explained in said specification No. 763,655that there is a time element in the firing of a gap by a given appliedvoltage. If the voltage is raised the time lag is shortened and viceversa if the voltage is lowered. Raising and lowering the voltage inconformity with a modulating signal thus enables the firing time lag tobe varied.

This may only be done effectively when the firing time lag, which canonly be varied within certain limits, is a substantial proportion of thepulse duration and therefore at the low pulse frequencies for whichthese simple arrangements are most suitable, a saw tooth pulse shape isgenerally preferable.

What is claimed is: i 1. A pulse distributor comprising an envelope, aplurality of electric gaseous discharge gaps each gap including twoelectrodes one of which is parallel, each pulse firing a successive gap,and a separate utilization device connected in series with each gap. 7

2. A pulse distributor according to claim 1 wherein said gaps include aplurality of cathodes each forming said one electrode of a separate,

gap, and separate leads extending from each of said cathodes throughsaid envelope.

3. A pulse distributor according to claim 2 wherein a separate outputtransformer is connected in series to each of said leads.

pulses are produced.

4. A pulse distributor according to claim 1 gence channels and separatedemodulating means arranged in the utilization device associated withseparate gaps to demodulate the pulses distributed to their respectivegaps.

7 A pulse distributor according to claim 1, further comprising a localpulse generator synchronized with the pulses applied to the gaps, andcoupled to said gaps, 'a plurality of gate circuits each associated witha separate one of said gaps and adapted to give an output only when apulse derived from the firing of the associated gap coincides with saidlocal pulses.

8. A pulse distributoraccording to claim 7 further including a sawtoothpulse shaper associated with said .local pulse generator and actuatedthereby, means for impressing an intelligence signal on each of saidgate circuits for combination with the sawtooth pulses, each of saidgaps being adapted to fire when the sawtooth and intelligence signalstogether reach a predetermined amplitude and to cease firing at the endof each sawtooth pulse whereby variable width output ALEC HARLEY REEVES.

References Cited in the file of this patent 550,856 Germany May 23, 1932

